Requirements

The Relational DAS requires that the SDO extension be installed.
The SDO extension requires a version of PHP 5.1, and the
Relational DAS requires a recent version that contains
an important fix for PDO. The most up-to-date information about
required levels of PHP should be found in the changelog for the
package on PECL. At the time of writing, though, the Relational
DAS requires the most recent beta level of PHP 5.1, that is
PHP 5.1.0.

The Relational DAS uses PDO to access the relational database,
and so should run with a variety of different relational databases.
At the time of writing it has been tested in the following configurations

MySQL 4.1.14, on Windows.
The Relational DAS operates correctly with the php_pdo_mysql
driver that comes with the pre-built binaries for PHP 5.1.0.

MySQL 4.1.13, on Linux. It is necessary to have the most up-to-date
PDO driver for MySQL, which comes built in to PHP 5.1.0.
It may be necessary to uninstall the usual driver that would have
come from PECL using
pear uninstall pdo_mysql.
You will need to configure PHP with the
--with-pdo-mysql option.

DB2 8.2 Personal Edition, on Windows.
The Relational DAS operates correctly with the
php_pdo_odbc driver that comes with the pre-built binaries for
PHP 5.1.0.

DB2 8.2 Personal Developer's Edition, on Linux.
The Developer's Edition is needed because it
contains the include files needed when PHP is configured
and built. You will need to configure PHP with the
--with-pdo-odbc=ibm-db2 option.

The Relational DAS applies changes to the database within
a user-delimited transaction: that is, it issues a call to
PDO::beginTransaction()
before beginning to apply changes, and
PDO::commit()
or
PDO::rollback()
on completion.
Whichever database is chosen, the database and the PDO driver
for the database must support these calls.